The increasing demand for computing, communications and information storage devices that are portable is evidenced by the development of smaller and smaller personal computers such as the portable, the lap-top, the notebook and the palm-top. Further, many specialized personal computing and communication devices such as personal digital assistants, foreign language translators, facsimile machines and mobile telephones have been introduced into the marketplace. All of these devices have the requirement for storage of significant amounts of information and, as a result, there has been continuing pressure to develop smaller, lighter, faster and more reliable information storage devices. In recent years technology has been pursuing two directions for the development of information storage devices to fulfill the needs of these products. The first direction has been the development of hard disk drives which utilize rotating magnetic disks and read/write transducers, a technology commonly referred to as "Winchester" technology. The second is the development of solid state semiconductor memory cards that utilize a technology known as "Flash" technology.
Smaller hard disk drives employing Winchester technology are being developed as evidenced by the drive described in U.S. Pat. No. 4,965,684 which is 1.0 inches in height; the drive described in U.S. Pat. No. 5,025,336 which is approximately 0.630 inches in height; the drive introduced to the market by KALOK, Inc. which is 0.5 inches in height; the drive introduced by MiniStor, Inc. which is 0.386 inches in height; and the drive introduced by Hewlett Packard which is 0.414 inches in height.
In addition to small size, the users of information storage devices want the device to be removable from the product to allow the transport of information between systems, to allow the device containing information to be protected or locked in a vault for security, and also, to provide a means for storing a duplicate copy of the information which is referred to as a "backup copy," that is--a copy that will be available if the original is lost or destroyed. Currently, the design of hard disk drives incorporates the control electronics on each drive. Although the drive can be removed from the product or system, it is clumsy to do so, damage to the control electronics and/or the drive itself represents a risk, and the cost of each unit is significant since each drive includes all of the control electronics, spindle drive motor and other major components thus making it expensive to be used as a "backup copy".
In attempting to continue reducing the height of Winchester hard disk drives, design engineers have been limited by the height of two major components in the drive. One is the spindle motor used to rotate the disks and the second is the voice coil actuator assembly which is used to position the read/write transducers at selected locations over the magnetic storage disk. Although progress has been made in reducing the height of these two required components, no design has been achieved which has resulted in a hard disk drive with a height less than those listed above.
Alternate design approaches (not using Winchester technology) have been employed in an effort to fulfill the needs of end users desiring to remove the information storage apparatus from the system. One design is that offered by the Iomega Corporation which utilizes a cartridge employing a flexible magnetic disk. The cartridge is removable from the drive mechanism and control electronics. This design approach has met with only limited success since the number of tracks per inch of magnetic disk space is limited due to the flexibility of the disk and the requirement to very accurately register the flexible disk relative to the read/write transducers when the flexible disk is inserted into the drive mechanism, thus the storage capacity of the device is limited and is not competitive with the storage densities achieved by Winchester hard disk drives. Further, the risk of losing information due to foreign material entering the cartridge is significant.
The SyQuest Corporation has introduced a design similar in concept to that of Iomega, except the removable disk cartridge incorporates a hard disk. This design is an improvement over the flexible disk concept, but still suffers from a capacity limitation due to the accurate registration required between the disk and the read/write transducers for high capacity. Contamination of the disk in the cartridge from foreign material with the resultant possibility of information loss is also a consideration and has limited the market acceptance.
Several other companies have attempted to greatly increase the storage capacity of flexible disks that are removable from the drive mechanism and control electronics. Perhaps the most creative design has been attempted by Insite Peripherals with the introduction of a flexible magnetic storage disk that writes and reads information with magnetic transducers, but employs a laser optical control servo system to control the position of the transducers over the recording track, thus attempting to greatly increase the number of tracks per inch of disk space. In spite of this novel approach, the storage capacity of the device has not proven to be competitive with classic hard disk Winchester technology. Further, the data transfer rate of 300 kilobits per second is considered relatively slow and the device has not been cost competitive. As a result it has not been well received in the marketplace and has not become a standard for either the transport or the backup of stored information.
Yet another approach to storing information is the use of the Compact Disk or CD ROM as it is called in the industry. This technology has been developed over a long period of many years by a large number of companies including such well known companies as SONY of Japan and Philips of The Netherlands. Compact disk technology employs a laser beam to write and read information on a rotating disk which has special coatings that are sensitive to the laser light. The CD ROM was first introduced as a read only device and received successful market acceptance for the distribution and playback of music and large data bases. Only recently have devices been introduced that will both write (record) and read (playback) information. The disks are rugged, reliable and can be easily removed from the device for transport. However, the system is sensitive to shock and vibration. Further, the time required to access the disk and write information is a very slow 300 milliseconds and is not considered competitive with Winchester technology which typically accesses the disk in 10 to 20 milliseconds.
In contrast to the rotating optical and magnetic disk approaches to information storage, the Flash Memory Card, which uses semiconductor technology, is robust, small in size (3.37 inches long by 2.13 inches wide and 0.129 inches in height), and is easily removable from the system. However, the information is stored on the memory card in a way that makes it difficult for the computer or other system to write and read the information. That difficulty has been resolved by the design of complex electronic circuits which make the memory card "look like" a hard disk drive to the computer. This additional electronics not only makes the memory card expensive, but also nullifies some of the space advantage that the memory card appeared to have as a result of its smaller size. In addition, the semiconductor integrated circuits used in the flash memory card are very expensive, costing many times the cost of a hard disk drive with an equivalent amount of information storage capacity.